The present invention relates to a device for forming and diffusing calibrated small volumes of liquid, referred to for convenience in the text below by the generic term xe2x80x9cdropsxe2x80x9d, serving in particular to produce drops with accurate control over drop size and drop number, for example in order to diffuse liquids into the atmosphere or onto a surface.
Numerous fields of activity exist in which it is necessary to have controlled quantities of liquid for delivery into the atmosphere which surrounds people or in their immediate environment, or onto their skin, or inside their bodies. Such liquids contain active principles, which is why diffusion thereof must be under control. The active principles can be for olfactive, medical, pesticidal, chemical, biological, etc., purposes.
A need thus arises to use a liquid substance in the form of drops in fields associated with medicine and well-being. Thus, in the context of certain treatments, active principles are diffused into the atmosphere or onto a portion of a patient""s body by spraying to enable the patient to feel the effects thereof in appropriate manner. Similarly, it can be advantageous to deliver calibrated drops into a medium where, after mixing or dissolving, the active principles carried by the drops produce their effect.
Similarly, substances having a beneficial or an agreeable effect are diffused by evaporation or by being sprayed, such substances being known for their olfactive effects (essential oils, perfumes, deodorants, etc.) or their cleansing effects (insecticides, disinfectants, neutralizing agents, etc.).
Other fields of application concerned by the invention include, amongst others: the study of liquids in the form of drops, depositing liquids in the form of droplets, activating liquids, etc., in various industrial, scientific, medical, or everyday-life contexts.
A variety of techniques exist for creating and diffusing drops or droplets. Most rely on the principle of interaction between a flow of gas and a liquid from which the drops are to be extracted. That principle is used in particular in conventional perfume sprays, in aerosol cans, and in paint guns.
Although they are simple to implement, those technique do not make it possible to produce drops that a are well calibrated or to produce drops at a rate that is controlled accurately. Furthermore, apparatuses operating on the principle of causing a gas and a liquid to interact are ill-suited to miniaturization, in particular because they need to be fed with propellant gas.
Techniques also exist whereby droplets are injected on the basis of electromechanical phenomena (such as the piezoelectric effect) or thermal phenomena (such as spraying by heater resistances, as used in particular for ink jet printers). Nevertheless, apparatuses relying on those techniques are relatively complex from the mechanical point of view, if only because in many cases they use numerous delicate moving parts. Furthermore, the quality of the calibration obtained for the drops is often given by a statistical distribution of drop size.
An object of the present invention is thus to provide a device of small dimensions that can be made at low cost, enabling drops of liquid to be produced in well-controlled manner.
To this end, the present invention provides a device for diffusing calibrated small volumes or drops of at least one liquid, the device being of the type comprising:
at least one displacement path for the liquid defined by a series of pairs of close-together surfaces enabling the liquid to be retained and to be moved from one pair of surfaces to another; and
means for applying an electric field between the pairs of surfaces in order to move the liquid from one pair of surfaces to another.
According to the invention:
the series of pairs of close-together surfaces defining a displacement path, co-operate to store the liquid, to form drops of liquid, and to move liquid drops to an outlet from said path leading towards a drop destination site; and
the means for applying an electric field apply a determined sequence of electric fields between the pairs of close-together surfaces so as to form drops of liquid from the liquid storage and so as to move them to the drop outlet.
In various optional embodiments, the present invention enables one or more of the following characteristics to be implemented in various technically feasible combinations:
said liquid is a liquid containing an active principle intended in particular for applications in generating odors, in cosmetics, in medical treatments, in hygiene, in chemistry, or in medical analysis;
said liquid contains at least one essential oil and/or a pheromone;
the device is arranged to convey the calibrated small volumes towards a zone of use which is associated with the outside of the device;
at least one pair of close-together surfaces constitutes at least one reservoir, a separation pad, and a pad for forming a small volume of liquid, co-operating to constitute an extractor of said small volume;
the reservoir comprises a volume for confinement by capillary action and interface tension between two close-together surfaces, at least one sector at the periphery of a liquid-retaining zone constituting extractor-forming means, and at least one face of the retaining zone being connected to liquid-feed means;
the extractor is constituted by a liquid-retaining zone adjacent to the reservoir, and it is constituted by two parallel faces that are close together so as to produce capillary and surface tension actions therebetween, the width of said zone relative to the displacement axis of the liquid being substantially smaller than its length, and more substantially smaller both than the width of the reservoir to which it is connected and than the width of the close-together surfaces of the displacement path for the calibrated volumes of liquid to which it is connected; and
the device is made up of at least two displacement paths enabling calibrated quantities 1, 2, 3, . . . , N of liquid to be extracted from at least two reservoirs and to be conveyed towards at least one other internal path of the device, the calibrated quantities 1 to N not necessarily having the same volume.
The destination site constitutes a site where the liquid transferred in this way is used and can thus benefit from all kinds of active or passive means for processing the drop. This destination site can be internal or external relative to the device of the invention.
The device of the present invention makes judicious use of the presence of electric fields distributed between the liquid source and the outlet, firstly to create a drop and secondly to conduct the drop towards the destination site by the dielectric effect.
The invention relates to all applications that require precision, such as measuring out and mixing liquids, in particular in cosmetics, biology, pharmacy, medicine, chemistry, or phytotherapy, and other industries, implementing for such purposes a so-called xe2x80x9clab on a chipxe2x80x9d.
By way of non-limiting example, the invention can be used to diffuse a wide variety of liquids containing odors as active principles, such as essential oils containing plant extracts.
When the means for applying an electric field comprise at least one pair of electrodes, the electrodes of a pair of electrodes can face each other and can be biased to create an electric field between each other, and they can be separated by a gap for confining liquid in the form of a more or less flattened drop. Under such circumstances, a pair of electrodes constitutes a capacitor, and the liquid, when present, constitutes the dielectric.
In embodiments of the invention, the volume (and to some extent the shape) of the drop is determined by the shape of the electrodes that come into contact with the liquid. Thus, it is possible to obtain uniform drops of volume that is determined very precisely by the volume constituted by the gap between the electrodes and by the outline of the facing, symmetrically shaped electrodes.
A plurality of electrodes or pairs of electrodes as mentioned above are preferably disposed in such a manner as to form a drop displacement path, the electrodes or pairs of electrodes being biased in controlled manner so as to cause at least one drop to move progressively towards the outlet.
In order to control the positions and the spreading of drops, it is possible to use either separately or conjointly both local surface treatment so as to obtain wettable and non-wettable interface tension effects for the surfaces, and different staged thicknesses between the pads provided with the electrodes and the remainder of the substrate surfaces (raised structures known as xe2x80x9cmesasxe2x80x9d).
An example of non-wetting treatment that can be used in the invention is treatment with the hydrophobic fluorine-containing silane of the C16H19F17O3Si type.
The volume of the drop that is extracted is determined essentially by the pairs of the electrodes on the path which act as an extractor of drops from the liquid source, said electrodes possibly being of dimensions that are different from the dimensions of the other electrodes as a function of the size of drop desired at the outlet.
In particular, the extractor can advantageously comprise an electrode or a pair of electrodes substantially narrower than the other displacement electrode(s), thus constituting a constriction in the displacement path.
When the device is made using pairs of storage electrodes and/or displacement electrodes, each pair comprises a first electrode and a second electrode, the first electrode being made on a first substrate and the second electrode being made on a second substrate.
The source can comprise liquid-storage means comprising a storage electrode or one or more pairs of storage electrodes enabling an electric field to be applied to the supply of liquid.
Liquid-supply means provided with electrodes can also be associated with a reservoir of greater volume for feeding them, thus making it possible, for example, to provide for the supply means fitted with electrodes to have some minimum capacity which is just sufficient to keep a particular dose of liquid available. This has the advantage of keeping the drop displacement path down to a strict minimum, given that it is more complex and expensive to fabricate, for given volume, than is the larger-volume reservoir. The device of the invention is advantageously made using the collective production means of microelectronics, where the cost price of such devices is directly proportional to surface area.
The reservoir is advantageously in the form of a removable or refillable cartridge or the like.
The drop outlet can comprise an orifice configured to enable the drops to flow to the outside or to allow them to evaporate at the orifice or to subject them to any heat, mechanical, electrical, etc. treatment causing them to be diffused.
The outlet orifice can advantageously comprise an electro-osmosis electrode. In this context, it should be observed that an electrode or a pair of electrodes at the outlet is also referred to as a displacement electrode, given that it also contributes to transfer by constituting the last link.
It should be observed that in certain applications, the outlet of the displacement path can be associated with a chamber or enclosure arranged inside the device and constituting the drop destination site.
The displacement path can be connected to one or more sources of liquid. When a plurality of liquid sources are connected to a common displacement path, at least one of the displacement electrodes or electrode pairs is connected upstream to a plurality of electrodes each capable of transferring a drop coming from a different source.
This configuration makes it possible to form individual drops coming from liquids having different sources. This embodiment of the invention thus makes it possible to mix a plurality of different liquids so as to constitute a single drop or a plurality of drops.
For each liquid source, the means for applying an electric field to form the individual drops from respective liquid supplies for the purpose of creating drops containing a mixture of liquids can themselves be calibrated independently from one another. In this way, when making a drop, it is possible to create a mixture comprising a plurality of different liquids, each liquid being present in a specific measured quantity.
In a preferred embodiment of the invention, the device is preferably substantially plane in structure and can be integrated in a thin assembly. The drop outlet can be arranged in one of the faces of the assembly or in one of its edges. Under such circumstances, it is possible to provide an outlet orifice from the device that is likewise formed in the edge of the device.